1. Technical Field
This invention relates to bulk trailers and more particularly to a system for removing a load out of the back of the trailer by wrapping a flexible floor around a powered drum at the discharge end of the trailer; the moving flexible floor pulls an ejector panel from the front of the trailer to the rear of the trailer; and where the efficiency of the discharge system is increased by closely matching the input power to the power required to move the load.
2. Description of the Prior Art
Bulk materials have been and continue to be transported by open-top transport semi-trailers. These trailers fit into several categories primarily based on the method of removing the load from the trailer body. There are several factors that determine how profitable a particular type of trailer will be in a particular operation. In general, truckers get paid for moving material from point A to point B; the more they can haul and the less time it takes them to haul it, that the more profitable their operation will be.
Since most localities legislate the maximum allowable vehicle weight, the weight of the truck and trailer become very important. Every pound of truck or trailer weight reduces the maximum payload by a pound. Another important factor is the speed with which the payload can be deposited at a job site. This is particularly important on short hauls where the turnaround time (the time it takes to get from the load site, to the dump site and back to the load site) may be 15 minutes or less. All things being equal, if the trucker can save one minute when depositing the load on a 15 minute turnaround time, two additional runs can be made in a single 8 hour day. This significantly increases the profitability of the trucking operation.
Another important part of the profitability picture in transporting materials is the availability (the amount of time the trailer is actually available for use, and not in the shop for repair) of the trailer. The availability of the trailer is commonly affected by its complexity. In general, the more parts there are, the more things there are to go wrong and the more often the trailer will be in the shop for repair.
Further, the initial cost of the trailer is a factor in the overall profitability of the trucking operation, as that initial cost must be amortized over a number of years and paid for out of profits made from hauling material.
Safety is also another issue that must always be considered. One of the biggest problems with long dump style trailers is stability when dumping. Tipping a trailer over because of unstable ground, sticking loads, and driver error are typical. Another problem is sealing the trailer so that the material they contain does not slip out onto the roadway. Most everybody has dealt with the rock chips in their windshields that this causes or worse. Therefore, it is very important to be able to seal the tailgate and other areas of the trailer where material could leak out.
The prior art falls into several types. The first is what is commonly referred to as walking floor® or shuffle floor unloading. These trailers eject the load by means of moving floor slats, typically made out of aluminum extrusions, steel, or even composites. These slats are grouped in sets of three across the floor. In other words, if there are 21 slats to make up the floor, slats 1, 4, 7, etc. belong to group one. Slats 2,5,8, etc. belong to group 2. Slats 3,6,9, etc. belong to group 3. Each of the groups of slats is connected to a hydraulic cylinder. To eject the load, all the slats are pushed out a certain distance, for example two feet. This moves the whole load rearward 2 feet. Then group 1 slats are retracted. Since, group 2 and 3 slats did not move, there is more friction holding the load from moving than group 1 slats generate when they slide back and the load stays put. Likewise, group 2 slats are pulled back while groups 1 and 3 are stationary. Likewise, group 3 slats are pulled back while group 1 and 2 slats are held stationary. Then the process is repeated. Shuffle floors have the disadvantage of being very heavy as there is, effectively, a double floor, the floor that supports the slats and the slats themselves. The shuffle floor is also quite slow. It is typical for such a floor to take 8 to 10 minutes to remove a load from a 48-foot trailer body. Maintenance can also be a problem, as there are a substantial number of moving parts. Even though there have been great strides in sealing the moving slats, material getting under the slats can still be a problem. Yet another problem was walking floor type trailers is that with particulate materials it is virtually impossible to completely clean out the trailer. Also, there are some materials, such as biosolids, that simply cannot be moved by this method. Shuffle floors also make inefficient use of the power available to them in that the floors operate at the same speed and have the same force available for moving the load when the trailer is full or empty.
Another method used to remove a load from a trailer is simply dumping. This method consists of having a hydraulic cylinder that either pushes the bed up directly, or operates a linkage that pushes the bed up. The most apparent problems with this type of trailer is that the center of gravity gets very high and can cause the trailer to tip over easily, especially if the ground is not flat or is unstable. Another problem is that loads can stick, and gravity is the only force trying to extricate the load from the trailer. If the load sticks, tipping the trailer over is much more likely. Also, many times granular loads need to be spread evenly on the ground, instead of just stockpiled. Again, the high center of gravity, when the trailer is up in the air, makes the possibility of tipping the trailer over while spreading a much larger problem.
Side dump trailers are similar to the trailer just explained, except that the body is dumped over to the side, instead of straight back. Many of the same stability problems are issues with side dump trailers. Further, because of the way side dump trailers must be designed, capacity is often an issue. Also, side dump trailers have difficulty spreading a granular load directly behind the trailer.
Yet another method used to remove the load from the trailer, utilizes a continuous conveyor belt. With different loads on the conveyor belt, it is sometimes difficult to keep the belt tracking correctly. Also, the belt must be continuous, and therefore must be spliced together by lacing, vulcanizing, or by some other means. This method of unloading has required a very expensive planetary drive that drives one of the rollers. Tensioning of the belt is a continuous problem, as the drive system depends on friction of the belt on the roller. This method is a very inefficient way to unload the trailer. Maximum torque is required when the trailer is full and the planetary drive has to be designed to generate enough torque to get the load moving. Yet, when the trailer is almost empty, the belt requires very little torque to move it, yet full torque is still available from the planetary drive. This can be mitigated to some extent by multi-speed gearboxes, but they increase the cost substantially. This also causes severe difficulty in trying to seal of the trailer. The top of the conveyor belt loop must be supported by the trailer floor and bottom of the conveyor belt typically runs under the floor. The belt must therefore enter and leave the volume contained by the trailer. All of the entrances and exits must all be sealed. A typical conveyor belt trailer may take two and a half to three minutes to eject a typical 48 ft. long trailer.
A flapper trailer is very similar to the continuous belt trailer just described, except that instead of a continuous conveyor belt, two chains and lateral rubber flaps are used. Maintenance costs are high. The flaps do not move the entire load all once, and therefore they are very inefficient. Like the conveyor belt method, full torque is always available even when it is not required. Another big problem with this type of trailer are the spaces for material to get trapped. The chains ride on top of a solid floor; the multiple rubber flaps effectively make any secondary floor above the solid floor. This space in between the two floors can end up being a repository for material that has been hauled. This is particularly a problem one first hauling on material such as gravel and later a material such as grain. If gravel has worked its way into this repository, then it has the possibility of contaminating the grain on future loads. Another difficulty with this type of trailer is that as the flaps, chains, and crossmembers the flaps are attached to come out of the load, and they can hold some of the material on them. This material is now able to fall off of these members, as they are now below the trailer floor, as the trailer moves down the highway.
Another type of trailer utilizes an ejector panel at the front of the trailer that is moved by a large telescopic cylinder. The cylinder required to eject a 48-foot long trailer is quite substantial and many times requires vertical supports simply to support the weight of the cylinder. Further, the force of the cylinder must overcome the friction of the material, due to its weight, on the floor and walls of the trailer. The force to eject the load may also increase the friction load as the pressure on the ejector panel increases the pressure of the material against the floor and sidewalls.
Another type of ejecting system is found in UK patent application 2351063. This patent application describes a trailer that utilizes a flexible floor that is attached at one end to a headboard and to a winch drum at the other end. The winch drum is rotated by means of a hydraulically operated planetary reducer mounted inside the drum. A sheave is mounted to the other side of the drum and wrapped with a cable. The cable goes through a compensating system, back up to the front of the trailer, around the sheave, and attaches to the headboard. To remove the load from the trailer, the winch drum is rotated, wrapping the flexible floor around the winch drum, which pulls the flexible floor and headboard toward the rear, dumping the material onto the ground. As the flexible floor is wound up onto the winch drum, cable is played out from the sheave that is mounted to the side of the drum. As the flexible floor winds up onto the drum, the radius of the drum changes. As the cable is played out from the sheave, the radius changes. Thus, the rate at which the flexible floor is wound onto the winch drum and in the rate the cable is played out are constantly changing. This requires a compensating system on the cable to make up for the differences. The planetary reducer required by the system is very expensive and is also very large, requiring a large winch drum. Further, the maximum torque required to get the belt moving when the trailer is full is still available to move the belt when the trailer is nearing empty. This is a very inefficient use of the power available. As previously explained, the drum gets larger as the flexible floor wraps up on the drum. The flexible floor is then pulled up off its supporting floor near the drum, allowing material to get under the flexible floor. Also, the tailgate cannot close until the entire flexible floor is unwound off of the drum. Further, it is very difficult to seal the drum by the tailgate. Whatever is used to seal the drum by the tailgate must compensate for the changing drum diameter or a gap must be left to allow for the change in diameter. Further, the cable length compensating system requires additional hydraulic and mechanical components to accomplish the return of the flexible floor and headboard to their original position. Further, this return is accomplished by the same motor that produces enough torque to move the load out, even though all it is doing is moving the headboard and unloaded flexible floor back into position. This is very inefficient and takes considerable time. Space considerations that allow the system of UK patent application 2351063 to be used on off-road vehicles may very well limit its application to over-the-road vehicles.
The foregoing challenges and design considerations, as well as others, are addressed by the present invention.